Packing containers of paper or plastic-coated paper are often manufactured from weblike-packing material which is provided with crease lines, emptying openings, tearing directions or print before it is divided into individual sheets or blanks and is converted by folding and sealing to finished packing containers. The majority of the working operations which are performed on the material web have to be carried out in register, that is to say, the working operation has to be done in a predetermined position on the material web in relation to the results of working operations already carried out previously. This is well-known in the technique of packaging and is achieved in a number of different ways.
When packing material webs are to be provided with cutouts, holes or the like which, for example, are to serve as pouring openings in the finished packing container, the pouring openings are punched out first at regular intervals in the weblike packing material. Thereafter some form of opening arrangement is applied which in its simplest form of realization may be constituted e.g. of a tear-off cover strip glued on over the prepunched pouring opening, so that the latter is closed in the desired manner. The application of the opening arrangements or cover strips hereby has to take place in register with the pouring openings.
The registry on application of the cover strips was achieved up to now in that the material web provided with pouring openings was made to pass a sensing device which was placed before the processing device at which the cover strips were applied. The distance between the point of application of the processing device and the sensing device corresponded to the distance between two pouring openings following each other in the packing material web or was equal to a multiple of that distance. By stopping the web each time a pouring opening is under the sensing device a cover strip can be applied over a pouring opening which previously has passed the sensing device, since it will then be right in front of the processing device. This arrangement functions well on the assumption that the distance between the emptying openings prepunched in the packing material web is correct. However, this is not always the case, and it may happen, moreover, in certain types of packing material that during the feeding the material stretches a little, which has the result that the cover strips will be placed slightly out of register with the emptying openings, that is to say they will go somewhat awry, and, under adverse circumstances, may end up partly outside the emptying openings.
It is desirable, therefore, to provide a method and an arrangement which make it possible to process a material web furnished with irregularities in complete register with the said irregularities, regardless of whether the irregularities vary slightly or whether the web tends to be lengthened or shortened during the handling.